1. Field of the Invention
The present invention relates to tuner units of TV sets. More particularly, the present invention relates to a tuner unit configured to operate without necessitating the use of high and low pass filters and other related components.
2. Description of the Related Art
In a conventional tuner unit of a TV set, where RF signals of both UHF and VHF channels as received by an antenna are all input to a single antenna input terminal, a single tuner unit which separately processes both UHF and VHF input signals with its UHF and VHF tuners is typically used. To do this, the antenna input terminal connects through an HPF (High Pass Filter) and a switch to a UHF tuner, and also connects through an LPF (Low Pass Filter) and a switch to a VHF tuner, so that a combination of an HPF (or LPF) and a switch allows only UHF (or VHF) input signals to reach the UHF (or VHF) tuner.
Specifically, with a conventional tuner unit, both an HPF and an LPF are necessary to divide the input signals from an antenna terminal into higher and lower frequencies. Two switches are also necessary to block unnecessary signal components which may pass through these filters.
FIG. 7 is a block diagram showing the system configuration of a conventional tuner unit.
In FIG. 7, an antenna 61 connects through an input terminal 62 to both an HPF 63 and an LPF 64, where the HPF 63 passes only UHF frequencies and the LPF 64 passes only VHF frequencies.
The output from the HPF 63 connects through a switch 65 to a UHF tuner 66. The output from the LPF 64 connects through a switch 67 to a VHF tuner 68. The output from the UHF tuner 66 and that from the VHF tuner 68 are combined and input to an intermediate-frequency amplifier circuit (IF circuit) 69. The switch 65 and the UHF tuner 66, or the switch 67 and the VHF tuner 68, are selected by a channel selector 71.
In other words, a conventional tuner unit requires an HPF 63 (or LPF 64) and a switch 65 (or 67) between an input terminal 62 and a UHF tuner 66 (or VHF tuner 68) as a pre-stage for the UHF tuner 66 (or VHF tuner 68). While the HPF 63, LPF 64, switch 65, and switch 67 are all indispensable in the conventional tuner unit to ensure satisfactory tuner performance (selectivity), they not only add to the cost of the tuner unit but also complicate its design and adjustment.
It is known that selectivity and other major characteristics of a tuner unit so depend on the pre-stage of the tuners that the performance of the pre-stage determines that of the whole tuner unit. Some conventional tuner units are shown in U.S. Pat. Nos. 4,598,425 and 4,499,495. These documents are incorporated herein by reference.
U.S. Pat. No. 4,598,425 defines a tuner unit which receives UHF, VHF and CATV signals collectively from a common input terminal through a network of a filter and a switch to either a higher-frequency tuner or a lower-frequency tuner to process higher and lower frequencies separately. The network is controlled depending on what channel a user selects.
U.S. Pat. No. 4,499,495 defines a tuner unit which receives UHF and VHF signals collectively from a common input terminal through a UHF/VHF selector switch to either a UHF tuner or a VHF tuner to process UHF and VHF signals separately. The mixed UHF and VHF signals pass through a filter network to the VHF tuner/but cannot reach the UHF tuner because of an open UHF/VHF selector switch before it when a VHF channel is selected; and pass through a closed UHF/VHF selector switch to the UHF tuner but cannot reach the VHF tuner because it is grounded by the UHF/VHF selector switch when a UHF channel is selected.
The present invention has been made in view of the above circumstances and has as an object to provide a simplified TV tuner unit which eliminates HPF 63 and LPF and 64, and switches 65 and 67, such as shown in FIG. 7, but is still capable of tuning in to either UHF or VHF signals satisfactorily.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.
To achieve the objects in accordance with the purpose of the invention, as embodied and broadly described herein, the invention includes a television tuner unit comprising a television signal input terminal providing both UHF and VHF input signals; a UHF tuner having a UHF resonance circuit for tuning to a desired channel in response to application of a tuning voltage to the UHF resonance circuit; a VHF tuner comprising a VHF resonance circuit for tuning to a desired channel in response to application of a tuning voltage to the VHF resonance circuit; and a resonance network, included in at least one of the UHF tuner and the VHF tuner, for controlling selection of which one of either the UHF input signals and the VHF input signals from the television signal input terminal are to be applied to the resonance circuit of the tuner in which the resonance network is included.
With a tuner unit according to the present invention, a common antenna input terminal connects directly to both UHF and VHF tuners of the tuner unit. The UHF and VHF tuners include as a pre- or post-stage an additional resonance network configured around a variable-capacitance diode to improve tuning performance.
More specifically, simply eliminating HPF and LPF filters and switches from a conventional tuner unit would result in a system in which not only wanted signals but also unwanted signals are input to the first-stage amplifier of a tuner, producing various combinations of beat and thereby adversely affecting tuning performance. Thus, the present invention provides a tuner with an additional resonance network to provide a result (obtain only wanted signals by attenuating unwanted ones) corresponding to that previously provided by the HPF and LPF and switches of the prior art.
As mentioned earlier, selectivity and other major characteristics of a tuner unit so depend on the pre-stage of the tuners that the performance of the pre-stage determines that of the whole tuner unit. To improve selectivity at the earliest stage, therefore, the present invention incorporates a frequency-selective element (for example, a variable-capacitance diode) as the pre- or post-stage of a resonance stage.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.